Adjustable table construction



July 16, 1957 B. HoPPE 2,799,544

ADJUSTABLE TABLE CONSTRUCTION Filed Aug. 3, 1954 4 Sheets-Sheet 1 BY Macha/m July 16, 1957 B. HoPPE 2,799,544

ADJUSTABLE TABLE CONSTRUCTICN Filed Aug. 5, 1954 l4 Sheets-Sheet 2 "Q t: N

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BY` 7. ,JLa/almucfhfL/Mm ATTORNEYS.

July` 16, 1957 B. HoPPE Y 2,799,544

ADJUSTABLE TABLE coNsTRuc'rIoN Filed Aug. s, 1954 4 sheets-sheet :s

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July 16, 1957 B. HoPPE Y 2,799,544

ADJUSTABLE TABLE coNsTRUc'rIoN United States Patent ADJUSTABLE TABLE CONSTRUCTION Boris Hoppe, Kew Gardens, N. Y. Application August 3, 1954, Serial No. 447,470

Claims. (Cl. 311-39) This invention relates to tables, and more particularly to tables having adjustable leg constructions for widening or narrowing the base supporting means for the table.

One of the objects of the present invention is to provide a novel table having a table leg construction which can be spread or closed as desired to provide an adequate degree of stability for table tops of varying sizes for such table.

A further object is to provide a novel table construction of the above character which is simultaneously adapted for use at different table top heights.

Another object is to provide a table construction of this general character wherein, without lowering the table top, the supporting leg means thereof can be spread apart by a substantial amount thereby increasing the stability of the table.

The invention in one aspect thereof is constituted by a table construction including a table top which is supported upon a main frame element therebeneath, the main frame element and table top being constructed and arranged for sliding movement, for example, from a central position to a position at one side of the main frame element thereby making room for the positioning of an additional leaf to the table which, if desired, can be hingedly secured to and comprise a part of the table top aforementioned. Or, if desired, a separate added leaf can be secured to the table top after so sliding the latter. In order to insure added stability of the table when the table top of larger area is used, a pair of leg elements is hingedly secured to the main frame element in such a manner that they may be spread when desired without substantially lowering the table top. The spreading apart of such leg elements is accomplished by angularly shifting same about their respective hinges or pivots with the aid of a` linkage which causes such angular shifting in equal amounts thereby maintaining the table top horizontal or substantially so during the spreading of the legs. Consequently articles already on the table top are not subject to falling olf. Such linkage comprises a pair of struts, each of which, at the lower extremity thereof, is pivotally secured to a leg element at a respective strut-leg pivot, the upper eX- tremities of said struts being pivoted to one another. The struts thus are in inverted V-form, and conjointly form a peak pivot at their upper pivotally connected extremities. Suitable guide means are provided for guiding the peak pivot in substantially vertical movement between the upper and lower limits, the leg elements obviously being spread apart when the peak pivot is at its lower limit and relatively closer when the peak pivot is at its upper Vlimit of motion. Such guide means may comprise, for example, a primary link, one extremity of which is pivotally secured to the main frame element, the other extremity of which is pivotally secured to the peak pivot. Suitable detent means can be employed for releasably holding such peak pivot in any of a plurality of positions between its upper and lower limits of motion. Alternatively, if desired, cam means may be employed for raising or lowering such peak pivot in response to sliding movement of the table top with respect to said main frame element.

Each of the two leg elements are hingedly secured at their upper extremities, as aforementioned, to the main frame element and each such leg element is provided with a hinged knee whereby the table can be adjusted in height to either a high position wherein said knees are straight or to a low position wherein the knees are bent at about right angles. Such knees are bendable from a straight condition outwardly toward the outer edge of the table top. In order to insure that the knees shall bend in coordination whereby the table top shall remain horizontal during the change from high to low (or vice versa), a linkage interconnects the upper portions of the leg elements insuring equal and opposite angular movement. This linkage cooperates with the aforedescribed strut construction for this purpose. At either the high, low or intermediate positions of the table top the leg elements can be spread as aforementioned to give greater stability to the table. However, the extent of such spreading is a maximum when the table top is at the high level and a minimum when the top is at the low level.

Various other objects and characteristics of my invention will become apparent from the followingI detailed description when read in connection with the accompanying drawings which form a part of the specication, it being expressly understood that the invention is not limited thereto, reference for this latter purpose being had to the appended claims.

In the drawings: v

Fig. 1 is a side elevation, partly in section and with parts broken away, of one form of `table construction embodying the invention;

Fig. 2 is a side elevation of the table of Fig. 1 but in a dilferent operating position;

Fig. 3 is a side elevation, partly in section and with parts broken away, of the table shown in Fig. 2 but in still another operating position;

Fig. 4 is a vertical sectional View of the table construction in Fig. 3, partly in section and with parts broken away, showing in end elevation a portion'of the linkage for controlling the position of the table legs;

Fig. 5 is a side elevation, also partly in section and with parts broken away, of the table of Fig. 1 in the low position, the table in Fig. 1 being in its high position;

Fig. 6 is a bottom View of the table shown in Fig. 5;

Fig. 7 is a perspective view of a portion of the linkagek positioned beneath the table top for assisting in controlling the high and low positions of the table and also for controlling spreading and closing of the leg elements thereof; i

Fig. 8 is a side elevation, partly in section and with parts lrokei away, of a modification of the table shown in Fig.

Fig. 9 is a side elevation, partly in section and with parts broken away, of a further modiication of the present invention.

Referring to the drawings in greater detail, with particular reference to the embodiment shown in Figs. 1 7, inclusive, a novel table construction 10 is shown cornprismg in general a table top 11 mounted upon a supporting main frame element 12 to which are hingedly secured a pair of leg elements 13 and 14. Such leg elements 13 and 14 are hingedly secured respectively at 15 and 16 to the main frame element 12 and are provided with hinged knees 17 and 18, respectively, which are capable of bending outwardly in such a manner that the table can be adjusted from its high position, as shown in Fig. l, to a low position, as shown in Fig. 5. The table thus in its high position (Fig. 1) may be more conveniently employed for such purposes as dining or cardl 3 playing whereas in the low position (Fig. 5) the table assumes the character of a so-called cocktail table.

In addition to the aforementioned features of adjustability to the high or low position, the novel table is constructed and arranged to accommodate table tops of adjustable size. For example, in the form shown in Fig. l, the table top 11 vconsists of two leaves 11a and 11b which are hingedly secured to one another at 11c and are folded double, that is, one leaf Vsuperimposed upon the other to provide a table top of preselectedsize which can be doubled in size by the simple expedient of unfolding the two leaves to assume a common plane. However, before such unfolding can occur, the double layer table top (Fig. l) should be shifted to oneside, for example, to the position shown in Fig. ,2, whereupon it can then be opened with both leaves coplanar. In such attitude the table top will have adequate support from the main frame element 12.

In the embodiment of Figs. 1 7, the tabletop 11.is constructed and arranged for sliding movement from a central position, as shown in Fig. l, to an offset position at one side of the main frame element, as shown in Fig. 2, thereby making room for the spreading open of the two leaves 11a and 11b whereby the leaf.11a kwill have adequate support on the top supporting surface of the main frame element 12. However, the invention is not limited to such a hinged slidable table top, itbeing possible to employ any suitable table top.

The means by which the table top 11 is associated with the main frame element 12 is Well illustrated in Fig. 4 and comprises oppositely and outwardly directed tongues 11d and 11e which are rigidly secured to the underside of leaf 11b and which engage the underside of shoulders 12a and 12b in sliding engagement.

In order to insure adequate stability of the table when the table top of larger area is used, namely, when the leaves 11a and 11b are coplanar, the pair of leg elements 13 and 14 are associated with the table in such a way that they can be spread without substantially lowering the table top, that is, such leg elements can be shifted angularly from the position in Fig. l to that shown in Fig. 2. Such spreading apart of the leg elements is accomplished by angularly shifting same about vtheir respective hinges 15 and 16 with the assistance of a linkage 19 which insures that there is a coordination of such angular shifting of the leg elements thereby maintaining the table top horizontal or substantially so during the spreading. Such linkage 19 includes a pairof struts 2G and 21, each of which at its lower extremity is pivotally securedto its respective leg element at 22 and 23. The upperextremities of the struts 29, 21 are pivotally secured to one another at 24. Such struts thus are in inverted V form `and conjointly form a peak pivot at their upper pivotally connected extremities.

Guide means are provided for guiding the peak pivot 24'to move substantially in vertical movement between upper and lower limits, the upper and lower limits of such motion being shown respectively in Figs. l and 2.

The leg elements obviously are spread apart when the peak pivot is at its lower limit and are relatively closer together when the peak pivot is at its upper limit of motion. Such guide means comprise, for example, a primary link 25, one extremity of which is pivotally secured at 26 to the main frame element 12 and the other extremity of which is pivotally secured to the peak pivot 24. A lower limit-stop 24a comprising a pin is provided beneath the peak pivot 24.

The aforementioned knees 17 and 18 will now be described, with particular reference to their ability to remain locked in straight or unbent condition despite the spreading or closing of the legs 13 and 14. The knee 17 is typical of the pair of knees and comprises Va hinge 27 (Fig. l) which associates the abutting upper and lower knee extremities 13a and 13b of the leg element 13. Such extremities together form an L joint wherein-a kneecap 13e (integral with the lower portion 13b) abuts against a reduced portion 13d integral with the upper portion 13a. The knees 17 and 18 tend to remain in their unbent or straight attitude (Figs. l and 2) by virtue of the speical positioning of their respective hinges at 27 and 28 as follows: Consider, for example, the hinge 27 which is positioned to the right of a straight line drawn between the hinge 15 and the supporting point 29 at the foot of the leg 13. The same is true with respect to the knee 18, that is, its hinge 28 is lto the left of a straight line drawn between its upper hinge 16 and a supporting point 30 at the foot thereof. This is well.illustrated in Fig. 2.

The holding of the knees 17 and 18 in their straight or unbent attitudes is also assisted by a linkage 31 which interconnects the two leg elements 13 and 14 in such a way that they shift angularly in equal and opposite amounts. The linkage 31is constituted by ya crossflink 32 which is pivotally secured at 33-to a bracket 34 which in turn is rigidly secured to the leg element 14. The opposite extremity of the link 32 is pivotally'associated at 35 with the outer extremity of an arm 36, the latter being rigidly secured at 37 to the angularly shiftable leg element 13.

In order resiliently to urge the leg elements 13 and 14 towards their straight or unbent conditions, a spring38 is employed which is secured at one extremity to the leg 14, for example, at the pivot 33, the other extremity of the spring being secured at 39 to the main frame element 12. Thus the force of the spring 38 urges leg element 14 in a clockwise direction (Fig. l) and the leg element 13 in a counterclockwise direction. However, the strength of spring 13 is preferably not greatenough to overcome the weight of the table top 11 and frame element 12 thereby to lift same from thelow to the high position.

The linkage will now be described, which automatically raises or lowers the peak pivot 24 of the linkage 19 in response to sliding movement of the table top 1'1 with respect to the main frame element 12. Such means comprise in this embodiment a cam device which is operatively associated with such peak pivot 24 whereby the latter is at its uppermost position when the table top is folded double and centered, as shown in Fig. l, but is in its lowermost position when the table top is slid to its righthand limit of motion (Fig. 2). For the above purpose, an inclined cam rail 40 is rigidly secured to the undersurface of the lower leaf 11b of the table top 11. The inclination of the cam rail 1G is effected by positioningthe lefthand extremity thereof (Fig. '1) farther away from the lower surface of'leaf'llb than the righthand extremity thereof.

The primary link 24 is angularly shifted by virtue of an operative interconnection with the inclined cam rail 40 effected by'means of cam link 41 which is at its lower extremity-pivotally secured to the primary link 25 at 42, the upper vextremity thereofihaving a cam following roller 43 secured thereto for engaging a groove 40a in the inclined cam rail 40. The cam'link `Lil is held in position for communicating thrust to the primary'link 19 with the aid of a link 44 which at'the vrighthand extremity thereof (Figs. l and 2) is pivotally secured at 45 to the main frame element 12, the left hand extremity thereon being pivotally secured at tot to the cam link 41. lt will be observed that a parallelogram is formed between the pivots 26, 42, 46 and 45.

If desired the 'particular'parallelogram linkage aforementioned can Vbe dispensedwith `and any other suitable means employed for associating'the vprimary link `19 with the inclined camrail 40. For exampleythelink 41 may be rigidly secured (instead of pivotally) to the primary link 25.

VIn Vorder'to insure the positive engagement between the groovedcam rail and the primaryV link 19, a linkage, asshown in Fig. 7, may be 'employed wherein the cam link 41y consists of two spaced but parallel links 41aY and 41b which have respectively secured thereto links 44a and 44b which perform the function of the aforementioned link 44. The cam rail 40 in Fig. 7 is of an I cross-section and thus is adapted for receiving two opposed rollers 43a and 43b, respectively pivotally secured to the cam links 41a and 41b.

The cam links 41a and 41b at their lower extremities are pivotally secured to a bifurcated primary link consisting of elements 25a and 25b which pivotally embrace the pivot rod 26 (Fig. 7) at one extremity of each and which are pivotally secured at 24to the peak pivot of the struts 20, 21.

In operation of the embodiment of Figs. 1-7, consider, for example, the table in its high position, as shown in Fig. 1, wherein a relatively small size table top is employed. When it is desired to increase the size of the tabletop, the folded leaves 11a and 11b are shifted from the position shown in Fig. 1 to the right to that shownin Fig. 2 thereby shifting the peak pivot 24 from its uppermost to its lowermost position (Fig. 2) by means of the cam rail 40, the cam link 41 and the linkage 19. The leg elements 13, 14 are thus shifted angularly outwardly about their respective pivots to the position shown in Fig. 2 wherein the distance between the leg elements is increased, illustratively, in excess of 50%. That is, the distance between the feet of the leg elements 13, 14 in Fig. 2 is about 50% greater than the distance between such feet when in the position shown in Fig. 1. After the table top 11 has been shifted to the position shown in Fig. 2, the uppermost leaf 11a can be angularly shifted in the direction of the arrow 47 so that it rests upon the upper surface of the main frame element 12 and is in a common plane with the lower leaf 11b (Fig. 3).

If desired, the table in the condition shown in Fig. 3

can be shifted from the high position shown (wherein the knees 17, 18 are straight) to a position wherein such knees are bent and the table is in its low position, as shown in Fig. 5.

The table top 11 (Fig. 1), of course, can be maintained in its centered position and the leg elements 13 and 14 bent whereby the table is moved to its low position, as shown in Fig. 5, the bending of the leg elements being precisely coordinated by means of the aforementioned linkages 19 and 31.

When the elements 13 or 14 are in their bent or low condition, as shown in Fig. 5, the table top 11 may be shifted from its relatively smaller size and centered position to the right to its offset position whereby the peak pivot 24 will be moved from the position shown in solid lines (Fig. to that shown in broken lines. This will effect a relatively smaller spreading of the lower portion of each of the leg elements 13 and 14 via angular movement thereof about the knee hinges 27 and 28, respectively. Such shifting of the peak pivot 24, as shown in Fig.` 5, thus can effect a substantially smaller spreading of the leg elements as compared to the extent of such spreading which occurs when the table is in its high position and the peak pivot is shifted with the legs in their fully extended or straight condition, that is, from the condition shown in Fig. 1 to that shown in Fig. 2. When the table is in its low position (Fig. 5), it is not necessary to spread the leg elements as much as it is when the table is in its high position (Fig. l). Thus the adjustable high and low feature of the novel table construction automatically accommodates the extent of spreading of the leg elements to the particular height of the table.

When the table is in its low position and the table top is folded double, as shown in Fig. 5, the uppermost extremities 48 and 49 of the knees 17 and 18 engage the lower surface of the lowerrnost leaf 11b. However, when lthe table top 11 is shifted to its offset position, the tongues 11d and 11e must be suitably interrupted, that is, a suitable portion thereof must be cut away to permit such upper extremities49 to pass therethrough and to engage 6 the undersurface of the leaf 11b when in such oset position. The upper extremity 48 of the other leg element 17 engages a suitable pin limit-stop 48a on the main frame element (Fig. 5) thereby to provide a firm support for the table top.

The form of the invention shown in Fig. 8 is similar to that shown in Fig. l with the exception that leg elements 50 and 51 are employed which are rigid and thus are not provided with knees. In this embodiment the linkage 31 is dispensed with, together with the spring 38. Struts 52. and 53 are provided which are analogous to struts Zt) and 21 and which are secured together at a peak pivot 54. The struts 52 and 53 are respectively pivoted at their lower extremities to the leg elements 50 and 51.

The leg element 50 is pivotally secured to the main frame element 12 by means of a hinge 55 which is secured to the outer surface of the leg element in such a manner that the upper extremity 50a of the leg element 50 acts as a limit-stop against angular movement counterclockwise beyond the position shown in Fig. 8 but permits angular movement clockwise from such position. The leg element 51 is analogously but reversely pivotally secured to the main frame element 12 by means of a hinge 56.

Primary link 57 is provided in Fig. 8 which is analogous in all respects to primary link 25 of Fig. 1 in that it guides the motion of the peak pivot 54 between its upper limit of motion (dened by any suitable limit-stop), as shown in Fig. 8, and a lower limit of motion defined by the limit-stop 58. An inclined cam rail 59 is secured to the bottom of the table top 11 in a manner similar to that shown in Fig. 1 with respect to cam rail 40 and is operatively connected to the primary link 57 by means of a cam link 60.

The cam link 60 may be constructed of two parallel elements analogous to that shown in Fig. 7 with respect to the cam link 41. Suitable cam follower roller means are secured to the upper extremity of the cam link 61 for following the groove in the cam rail 59.

The embodiment of the invention shown in Fig. 9 is identical to that shown in Fig. 8 with the exception that the cam rail 59 and the cam link 60 are omitted and a table top 62 is employed which may or may not be slidably secured to a main frame element 63. The leg elements 64 and 65 are employed which are similar to leg elements 5) and 51 and are respectively secured to the main frame element 63 by means of L-shaped bracket means 66 and 67 and pivots 68 and 69 respectively. The longitudinal axes of the leg elements 64 and 65 are thus offset or removed from the pivots 68 and 69. The upper surfaces of the L-shaped bracket means 66 and 67 serve as limit-stops to prevent angular movement beyond the perpendicular positions of the leg elements 64 and 65v respectively counterclockwise and clockwise.

Struts 70 and 71 are pivotally secured at 72 and73 respectively to the leg elements 64, 65 and the upper extremities thereof form a peak pivot 74 which is guided by means of a primary link 75 pivotally secured to the main frame element 63 at 76 and in a manner identical to the primary link 25 (Fig. l).

The lower limit-stop 77 restricts the vertical movement of the peak pivot 74 in a downward direction and is so positioned that the pivots 72 and 73, if desired, may shift angularly from the position shown in Fig. 9 outwardly to a point beyond the perpendicular dropped from the respective pivots 68 and 69.

The upper limit-stop for pivot 74 can comprise the underside of table top 62. Such upper limit-stop can be dispensed with and only the L-shaped bracket means can be employed for this purpose.

lt is possible by means of the embodiment of either Figs. 8 or 9 to widen the base, that is, the distance between the feet of the leg elements illustrativelyA 75% without lowering the level of the table top. A broader table top can thus be employed which, if desired, may have hinged drop leaves. Of course, the feet can be spread farther apart but the table topv may be lowered thereby.

What is claimed is:

l. In `a table construction, a table top; a main frame element supporting in horizontal attitude the aforementioned table top, said main frame element being situated beneath said table top; a pair of leg elements each having foot portions, said leg elements at the upper extremities thereof being hingedly secured to said main frame element, said leg elements being spaced from one another and acting in combination supporting said table top in horizontal attitude in response to the resting of the foot portions of such leg elements on a horizontal surface; means for operatively interconnecting said table top and said main frame element for relative sliding movement between selected limits and in a selected direction, and a linkage for controlling the angular position of said leg elements relative to one another including: a pair of struts, each being pivotally secured at its lower extremity to its respective leg element near the lower region of the latter, the upper extremities of said struts being pivotally connected with one another at approximately the level of said main frame element thereby forming a peak pivot, said struts being in inverted V-form, the distance between the foot portions of said leg elements being changeable in response to raising or lowering of such peak pivot; a primary link interconnecting said peak pivot with a pivot mounted on said main frame element; and cam means for angularly shifting said primary link in response to sliding movement of said table top with respect to said main frame element, the distance between said foot portions of the leg elements being alterable in response to such sliding movement.

2. In a table construction, a table top; a main frame element for supporting such table top, means for operatively interconnecting said frame element and table top for relative sliding movement in a selected direction; said frame element pivotally mounting a pair of leg elements in spaced relationship; a linkage for controlling the angular position of said leg elements in coordination with one another and about their respective pivots including a pair of struts, each strut being pivotally secured at its lower extremity by means of a lower pivot means to its respective leg element, the upper extremities of said struts being pivotally associated with one another by upper pivot means comprising a peak pivot, said struts being in inverted V-form, the angular position of said leg elements about their respective pivots being changeable in response to vertical movement of such peak pivot said leg elements being spreadable and closable in response to such peak pivot movement; and means for guiding said peak pivot in substantialiy vertical movement.

3. In a table construction, a table top; a main frame element for supporting such table top; said frame element pivotally mounting a pair of leg elements in spaced relationship, each of said leg elements being provided with a hinged knee intermediate the upper and lower extremi ties thereof, each of said leg elements being constituted by a primary portion above the knee and a secondary portion below the knee, linkage means for operatively inter connecting the primary portions of said leg elements whereby said primary portions are angularly shiftable in equal and opposite amounts; a pair of strut elements re spectively connected at their lower extremities to respective lof said secondary portions of leg elements, said struts being pivotally associated at their upper extremities thereby to form peak pivot means; and means for guiding said peak pivot means in substantially vertical movement, said leg elements being angularly shiftable about their main frame element pivots in coordination in equal and opposite amounts in response to such movement of said peak pivot means, said leg elements then being in substantially straight condition; the secondary portions of said afffafstta` leg elements also being analogously angularly shiftable about their respective knees in coordination in equal and opposite amounts in response to movement of said peak pivot means, said leg elements being bent at their respective knees, the extent of such angular movement of said leg elements when in a straight condition being substantially greater due to a given amount of movement of said peak pivot means as compared to the extent of angular movement of the secondary leg elements when the knees thereof are bent.

4. In a table construction, a table top; a main frame element for supporting such table top; said frame element pivotally mounting a pair of leg elements in spaced relationship, -said leg elements supporting the table top in horizontal position; each of said leg elements being provided with a hinged knee intermediate 4the upper and lower extremities thereof, each of said leg elements, by virtue of its respective knee, being bendable from a substantially straight position outwardly of the vertical center line of the table whereby said knees bend away from one another, each of lsaid leg elements being constituted by a primary portion above the knee and a secondary portion below the knee, the table resting upon the secondary portion of said leg elements in response to knees thereof being fully bent; linkage means for operatively interconnecting the primary portions of said leg elements, said primary portions being angularly -shiftable in equal and opposite amounts by said linkage means; a pair of strut elements respectively connected at their lower extremities to respective of said secondary portions of said leg elements, said struts being pivotally associated at their upper extremities thereby to form a peak pivot; and means for guiding said vpeak pivot in substantially vertical movement, said leg elements when in a straight condition being angularly shiftable about their main frame element pivots in coordination in equal and opposite amounts in response to movement of said peak pivot; the secondary portions of said leg elements also being analogously angularly shiftable about their respective knees in coordination in equal and opposite amounts in response to movement of said peak pivot, said leg elements being bent .at their respective knees; the extent Iof such angular movement of said leg elements when in a straight condition being substantially greater responsive to a given amont of movement of said peak pivot as compared to the extent of such angular movement Iof the secondary leg elements when the knees thereof are bent.

5. In a table construction, a table top; a main frame element for supporting said table top, a pair of leg elements pivotally mounted upon said frame element in spaced relationship; each of said leg elements being subdivided into a primary upper portion and a secondary lower portion interconnected by a hinged knee, such hinged knee having a iimit-stop for preventing angular motion in one direction when the primary and secondary portions thereof are in a relatively extended position but having means for permitting angular motion in an opposite direction, the hinge of each of said knees being `offset with respect to a line between the foot of each of said leg elements and the hinge connecting same to said main frame element, the primary and secondary portions of each of said legs being releasably held in such relatively c extended position; `a linkage for interconnecting the means for guiding said upper pivot means in substantially' vertical movement for controlling the relative angular positions of `said leg elements.

References Cited inthe le of this patent UNITED STATES PATENTS Hofman Ian. 28, 1873 Tiernann Dec. 29, 1874 Owens Nov. 3, 1914 Ulp June 25, 1918 Metzler Oct. 10, 1933 Kovats Oct. 9, 1934 10 Lapeyre Mar. 10, 1936 Perl Mar. 31, 1936 McFall Apr. 4, 1939 Roberts Feb. 22, 1949 Hoppe Mar. 6, 1951 Hoppe Mar. 6, 1951 Hoppe Dec. 18, 1951 Howe Aug. 19, 1952 FOREIGN PATENTS Sweden Oct. 31, 1938 

